Optical, or optic, switches have been available for some time. As is well known, optic switches are analogous to electrical switches: a typical optic switch has an input port and at least one output port, wherein the ports can be connected to optic fibers. When the switch is activated, the input port and a selected output port are "coupled" so that light received at the input port is routed to the appropriate output port. There are single "pole", single throw optic switches; single "pole", double throw switches; and so on.
Optic switches have been used in various settings. For example, optic switches are extensively employed in optic fiber communication systems. In addition, optic switches can be used to provide redundant optic paths. While redundant optic paths are often implemented using optic couplers which permanently divide the incoming light between two outgoing paths, this practice can result in a reduced signal-to-noise ratio. Optic switches, on the other hand, can alternatively direct all of the light from one path to another to achieve path redundancy while maintaining a high signal-to-noise ratio.
Optic switching devices are also generally important to optoelectronic connectors, such as repeaters and tranceivers in optic communication links. For example, optic switches can be used to automatically switch out faulty devices in a communications network.
Generally, there are two types of optic switches, mechanical (electro-mechanical) and solid state.
Mechanical optic switches require little power in switching and are passive while maintaining position. Unfortunatley, mechanical switches typically take at least one millisecond to switch the direction of a guided wave. Further, due to their inherent lack of precision, mechanical switches are really only suitable for multimode optic fibers having large core diameters (typically approximately 50 to 100 microns).
The sluggishness of the typical mechanical optic switch cannot be tolerated in many instances. Also, single mode fiber systems compatible with fiber core diameters of approximately five microns are becoming more prominent, placing very stringent alignment tolerances which mechanical switches cannot satisfy.
Thus, fast, precise solid state optic switches have been developed. A solid state optic switch preferably possesess the following characteristics: (1) it completely redirects the guided light beam into the selected optic path; (2) it accommodates accurate optic fiber to switch alignment, and matching of the optic fiber and switch light guide modal field profiles (displaying low loss coupling between the fibers and the switch); (3) its operation is independent of light polarization (i.e., works equally well for TE and TM modes); (4) the power required for switching is low; (5) the switch is "passive" while maintaining position; (6) the switch operates reliably; and (7) the switch is rugged.
One type of solid state optic switch uses the electro-optic effect to control the refractive index in a bounded region. Guided light incident on the bounded region will transmit undeflected to a first output port when the index is the same as that of the waveguide. Proper application of an electric field to the bounded region will change the refractive index resulting in total internal reflection (TIR) of the guided light beam to a second output port. Such a TIR switch has been fabricated in lithium niobate (LiNbO.sub.3) by Tsai et al, as reported in "Optical Channel Waveguide Switch and Coupler Using Total Internal Reflection," IEEE Journal of Quantum Electronics, Vol. QE-14, No. 7, July 1978, pp. 513-517.
Solid state optic switches are particularly useful due to their potential compatibility with single mode or monomode optic systems. In order to efficiently and easily incorporate an optical switch in a single mode optical fiber system, the transverse dimensions of the integrated optic waveguide must generally be on the order of the optical fiber core diameter. That is, the effective width and thickness of the switch's waveguide must be approximately 5 to 10 microns, even if the dimensions of the switch's waveguide matches that of the single mode fiber, the optic fibers must be precisely aligned with the waveguide to maximize coupling efficiency.
The present invention is directed primarily to the coupling problem discussed above. The invention includes a solid state optic switch which is particularly suitable for single mode optic systems, and the invention substantially eliminates the coupling problem discussed above.